Investigation of the effect of striated strands on the AC losses of 2G Roebel cables

Abstract

The assembly of meander shaped coated conductor tapes by the Roebel technique is a promising way to manufacture high current cables with low ac losses. The application of longitudinal striations to the single strands can be an option to create a filament structure for further possible reduction of the ac losses. Due to the complex Roebel strand geometry, it was important to identify a reliable technique to produce such structures using a picosecond-infrared (IR) laser for the groove etching process. We analyzed the effects of the filament structure on the magnetization ac loss behavior by comparing the losses of a cable with striated strands with those of a reference one with non-striated strands. The ac loss reduction in the Roebel cable with striated strands was confirmed. The measured magnetization loss of the 125 mm striated single strand is five times lower than that of the non-striated one. In the case of the cable sample the loss reduced by a factor of three, but not in the whole interval of amplitudes of the applied magnetic field. We also compared the results with those for a cable with insulated striated strands: they seem to indicate that the coupling currents occur mostly between the filaments, not between the strands.

Measurement and Numerical Evaluation of AC Losses in a ReBCO Roebel Cable at 4.5 K

“…There have already been several reports on the magnetization loss in Roebel cables, measured at the University of Kyoto [15], Industrial Research Ltd [16], [17], [18], Ohio State University [19], [20] and KIT [21], [22], [22]. However data is at 77 K and at frequencies above 10 Hz (in most cases the angular dependence is not considered).…”

AC Loss and Coupling Currents in YBCO Coated Conductors With Varying Number of Filaments

“…In the past few years, several groups have investigated the effectiveness of creating filaments by laser ablation for reducing AC losses. This has been done with various techniques: laser scribing [5]- [10], chemical etching [11], [12], mechanical scratching of the buffer layers [13], lift-off process with photoresist mask technique [14], dry etching [15], inkjet printing [16] or the combination of laser scribing and chemical etching [12]. Most of these techniques are developed for short samples only, with lengths between 10 cm and 1 m. The exception is [17], where the authors developed a reel-to-reel striation process for 500 m of tape up to 5 filaments.…”

The EuCARD-2 Future Magnets European Collaboration for Accelerator-Quality HTS Magnets

“…5, provides also: i) easy access to 10 kA class current cable; ii) ability of bending also in small radius (R ≅ 20 mm); iii) copper amount can be easily controlled for stabilization and protection, by adding Cu tapes. Striation, through laser ablation as investigated by KIT [37] on meandered tapes for Roebel cabling, may help in reducing magnetization by persistent current, if the joints will not act as short circuit. This point needs to be carefully investigated.…”